select: reject invalid file descriptors

POSIX requires invalid file descriptors to be detected rather than
silently ignored.  FreeBSD 8.2 detects if fd 0 has been closed
and appears in a set while fd 1 is still open, but mistakenly
optimizes and refuses to check any fds in the set beyond the
maximum open fd.

* m4/select.m4 (gl_FUNC_SELECT): Probe for FreeBSD bug.
* lib/select.c (rpl_select) [!win32]: Work around it.
* modules/select (Depends-on): Add dup2.
* doc/posix-functions/select.texi (select): Document this.

1 files changed, 19 insertions, 0 deletions

diff --git a/lib/select.c b/lib/select.c
index 4db09a353d..1ff6652c65 100644
--- a/lib/select.c
+++ b/lib/select.c
@@ -507,6 +507,8 @@ restart:
 
 #include <sys/select.h>
 #include <stddef.h> /* NULL */
+#include <errno.h>
+#include <unistd.h>
 
 #undef select
 
@@ -514,6 +516,23 @@ int
 rpl_select (int nfds, fd_set *rfds, fd_set *wfds, fd_set *xfds,
             struct timeval *timeout)
 {
+  int i;
+
+  /* FreeBSD 8.2 has a bug: it does not always detect invalid fds.  */
+  if (nfds < 0 || nfds > FD_SETSIZE)
+    {
+      errno = EINVAL;
+      return -1;
+    }
+  for (i = 0; i < nfds; i++)
+    {
+      if (((rfds && FD_ISSET (i, rfds))
+           || (wfds && FD_ISSET (i, wfds))
+           || (xfds && FD_ISSET (i, xfds)))
+          && dup2 (i, i) != i)
+        return -1;
+    }
+
   /* Interix 3.5 has a bug: it does not support nfds == 0.  */
   if (nfds == 0)
     {